Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ENDODERM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2000

A post-mid-blastula transition requirement for TGFbeta signaling in early endodermal specification.

In Xenopus, endodermal cell fate is determined gradually from late blastula to early gastrula stages; cell-cell interaction plays an important role in this process. Here we use a cell dissociation assay to show that extracellular signaling is required continuously before endoderm determination. Activin and Vg1, but not BMP2 or basic FGF, rescue the expression of endodermal markers in dissociated cells when provided at the mid-blastula transition (MBT, the time in which zygotic transcription begins). Removal of exogenously added activin or Vg1 before MBT results in reduction of endodermal gene expression in dissociated vegetal cells. In vivo, endogenous endodermal markers are reduced in vegetal explants when activin-like signaling is blocked with dominant negative receptors. VegT, a maternal transcription factor shown to be critical for endoderm specification, relies on an active TGFbeta pathway to induce endoderm in animal caps. These results indicate that TGFbeta signaling may be activated by the maternally expressed VegT to participate in endoderm determination. In addition, VegT function seems to be required in parallel with the TGFbeta pathway, as overexpression of activin does not relieve endoderm repression by a dominant negative VegT mutant in vegetal cells. Our data suggest that maternal VegT first activates a zygotic TGFbeta signal, then cooperates with this signal to determine the endodermal cell fate.

Activins↗
PubMed1996

Anterior primitive endoderm may be responsible for patterning the anterior neural plate in the mouse embryo.

BACKGROUND: After implantation, the basic body plan of the mammalian embryo is established during gastrulation when the epithelial founder tissue of the fetus, the epiblast, gives rise to new tissues by ingression through the primitive streak. Formation of the primitive streak defines the caudal aspect of the embryo and thus the anteroposterior axis. Further patterning of this axis has been attributed to signals produced by tissues arising from the primitive streak, and in particular the mesendoderm located along the midline of the embryo is thought to be responsible for the correct anteroposterior subdivision of the neurectoderm as it begins to form the central nervous system (CNS). RESULTS: In situ hybridization studies show that the onset of expression of the homeobox-containing gene Hesx1 coincides with the formation of the primitive streak, but occurs on the opposite side of the embryo, in a small domain of anterior endoderm. Lineage tracing using a lipophilic fluorescent label shows that the first endoderm cells to express Hesx1 are not destined to contribute to the future embryo, but instead belong to the primitive endoderm lineage and will be displaced by definitive endoderm arising from the primitive streak during gastrulation. Approximately 24 hours after Hesx1 transcripts are first detected in the endoderm, they start to appear in adjacent ectoderm that gives rise to the most anterior component of the developing CNS, the prosencephalon, which continues to express Hesx1. Eventually, Hesx1 transcripts are detectable only in Rathke's pouch as the pituitary starts to develop. Removal of endoderm cells expressing Hesx1 during the earlier stages of gastrulation either prevents or severely curtails the later expression of Hesx1 in ectoderm and neurectoderm, but does not affect gene expression in more caudal regions of the developing CNS. CONCLUSIONS: As overt anterior pattern is present in the visceral embryonic endoderm prior to formation of any axial mesendoderm, a mechanism for bestowing anterior pattern must exist which is independent of primitive streak descendants. Furthermore, correct molecular patterning of the most rostral neurectoderm appears to depend on the presence of this anterior visceral embryonic endoderm during the early stages of gastrulation. We propose that primitive endoderm is responsible for the initial induction of rostral identity in the embryo, and in particular for the correct definition of the future prosencephalic neurectoderm. Subsequently, this identity will be reinforced and maintained by axial mesendoderm when it displaces the visceral embryonic endoderm during the course of gastrulation.

Animals↗
PubMed2002

Ras/MAPK pathway confers basement membrane dependence upon endoderm differentiation of embryonic carcinoma cells.

The formation of extraembryonic endoderm is one of the earliest steps in the differentiation of pluripotent cells of the inner cell mass during the early stages of embryonic development. The primitive endoderm cells and the derived parietal and visceral endoderm cells gain the capacity to produce collagen IV and laminin. The deposition of these components results in the formation of basement membrane and epithelium of the endoderm, with polarized cells covering the inner surface of the blastocoels. We used retinoic acid-induced endoderm differentiation of stem cell-like F9 embryonic carcinoma cells to study the role of the Ras pathway and its regulation in the formation of the visceral endoderm. Upon endoderm differentiation of F9 cells induced by retinoic acid, c-Fos expression, the downstream target of the Ras pathway, is suppressed by uncoupling Elk-1 phosphorylation/activation to MAPK activity. However, attachment to matrix gel greatly enhances the activation of MAPK in endoderm cells but not in undifferentiated F9 cells. Enhanced MAPK activation as a result of contact with basement membrane is able to compensate for reduced Elk-1 phosphorylation and c-Fos expression. We conclude that endoderm differentiation renders the activation of the Ras pathway basement membrane dependent, contributing to the epithelial organization of the visceral endoderm.

Animals↗
PubMed1994

Fetal endoderm primarily holds the temporal and positional information required for mammalian intestinal development.

In rodents, the intestinal tract progressively acquires a functional regionalization during postnatal development. Using lactase-phlorizin hydrolase as a marker, we have analyzed in a xenograft model the ontogenic potencies of fetal rat intestinal segments taken prior to endoderm cytodifferentiation. Segments from the presumptive proximal jejunum and distal ileum grafted in nude mice developed correct spatial and temporal patterns of lactase protein and mRNA expression, which reproduced the normal pre- and post-weaning conditions. Segments from the fetal colon showed a faint lactase immunostaining 8-10 d after transplantation in chick embryos but not in mice; it is consistent with the transient expression of this enzyme in the colon of rat neonates. Heterotopic cross-associations comprising endoderm and mesenchyme from the presumptive proximal jejunum and distal ileum developed as xenografts in nude mice, and they exhibited lactase mRNA and protein expression patterns that were typical of the origin of the endodermal moiety. Endoderm from the distal ileum also expressed a normal lactase pattern when it was associated to fetal skin fibroblasts, while the fibroblasts differentiated into muscle layers containing alpha-smooth-muscle actin. Noteworthy, associations comprising colon endoderm and small intestinal mesenchyme showed a typical small intestinal morphology and expressed the digestive enzyme sucrase-isomaltase normally absent in the colon. However, in heterologous associations comprising lung or stomach endoderm and small intestinal mesenchyme, the epithelial compartment expressed markers in accordance to their tissue of origin but neither intestinal lactase nor sucrase-isomaltase. A thick intestinal muscle coat in which cells expressed alpha-smooth-muscle actin surrounded the grafts. The results demonstrate that: (a) the temporal and positional information needed for intestinal ontogeny up to the post-weaning stage results from an intrinsic program that is fixed in mammalian fetuses prior to endoderm cytodifferentiation; (b) this temporal and positional information is primarily carried by the endodermal moiety which is also able to change the fate of heterologous mesodermal cells to form intestinal mesenchyme; and (c) the small intestinal mesenchyme in turn may deliver instructive information as shown in association with colonic endoderm; yet this effect is not obvious with nonintestinal endoderms.

Aging↗
PubMed1997

end-1 encodes an apparent GATA factor that specifies the endoderm precursor in Caenorhabditis elegans embryos.

The endoderm in the nematode Caenorhabditis elegans is clonally derived from the E founder cell. We identified a single genomic region (the endoderm-determining region, or EDR) that is required for the production of the entire C. elegans endoderm. In embryos lacking the EDR, the E cell gives rise to ectoderm and mesoderm instead of endoderm and appears to adopt the fate of its cousin, the C founder cell. end-1, a gene from the EDR, restores endoderm production in EDR deficiency homozygotes. end-1 transcripts are first detectable specifically in the E cell, consistent with a direct role for end-1 in endoderm development. The END-1 protein is an apparent zinc finger-containing GATA transcription factor. As GATA factors have been implicated in endoderm development in other animals, our findings suggest that endoderm may be specified by molecularly conserved mechanisms in triploblastic animals. We propose that end-1, the first zygotic gene known to be involved in the specification of germ layer and founder cell identity in C. elegans, may link maternal genes that regulate the establishment of the endoderm to downstream genes responsible for endoderm differentiation.

Amino Acid Sequence↗
PubMed2000

Repressive and restrictive mesodermal interactions with gut endoderm: possible relation to Meckel's Diverticulum.

The midgut and hindgut endoderm of the mouse embryo give rise to the intestinal epithelium, yet it is not known how the intestinal program is chosen in contrast to other endoderm-derived cell types. Previous tissue explant studies with embryos at 8.5 to 11.5 days gestation (d) showed that when the gut mesoderm is removed from the prospective intestinal endoderm, the endoderm activates the expression of liver-specific genes such as serum albumin, demonstrating the endoderm's pluripotence. This reversible repression of liver genes does not affect the expression of the endodermal transcription factors HNF3 and GATA4, nor these factors' ability to engage target sites in chromatin. We have now found that at 13.5 d, the mesoderm gains a second inhibitory activity, resulting in the irreversible loss of expression of HNF3 (Foxa2) and GATA factors in the endoderm and the absence of factors binding to their target sites in chromatin. The second inhibitory activity causes the endoderm to lose the potential to activate a liver gene, and this restriction precedes the normal cytodifferentiation of the intestinal epithelium. In summary, two inhibitory interactions with mesoderm successively restrict the developmental potential of the gut endoderm, leading to intestinal differentiation. We also observed rare gut bud structures in midgestation embryos that appear to represent murine examples of Meckel's Diverticulum, a congenital abnormality in human development. The absence of restrictive mesodermal interactions could explain how Meckel's diverticula express diverse non-intestinal, endoderm-derived cell types.

Albumins↗
PubMed1991

[Morphological and functional features of endodermal cells in rat yolk sac, with special reference to the fetal macrophage differentiation].

Morphological and functional features of the yolk sac endodermal cells with special reference to the fetal macrophage differentiation were investigated morphologically under the light and electron microscopes and immunologically with the antigen phenotypic analysis and the phagocytic activity-test, using the syngeneic DA rat-embryos from 8 to 16 days of gestation. Based on the staining property with toluidin blue and the ultrastructural features, the endodermal layer from day 8 to 16-yolk sacs has been known to consist of two kinds of cell type; 10% "clear" cells with clear cytoplasm and 90% "dark" cells with dark cytoplasm. Numerous primary lysosomes, phagolysosomes, lipid droplets and coated vesicles distributed preferentially in the supranuclear portion of endodermal cells. A broad intercellular space was found between "clear" cells and "dark" cells, indicating the loose intercellular binding. It was often found that "clear" cells tend to migrate from the endodermal layer into the mesenchymal layer, where the poor development of basement membrane was seen between them. Cells phagocytosing red blood cells, that resemble morphologically "clear" cells, were also observed in the fetal liver. At ten hours after latex-injection into the yolk sac cavity of 14 days embryos, some cells which phagocytosed latex beads in their cytoplasm were found in the endodermal layer, and also in the liver tissue and loose connective tissue of fetus. These cells were stained positively with monoclonal antibody Mar3 which recognizes preferentially rat-mononuclear phagocyte system. In vitro-latex uptake of separated endodermal cells was also demonstrated by the culture-study of endodermal cell suspension. The present findings indicate that the yolk sac-endodermal layer derived from the proximal endoderm consists of at least two kinds of cell-population with a great similarity to tissue macrophages in morphological and functional senses, and support the concept that some cell-populations of endodermal layer may migrate into fetal tissue and are closely related to the differentiation of fetal macrophages and their precursors.

Animals↗
PubMed1981

Cell interactions and endoderm differentiation in cultured mouse embryos.

Morphological and biochemical evidence is presented that the visceral extraembryonic endoderm of the 6.5-day mouse embryo will differentiate into parietal endoderm when cultured in contact with extraembryonic ectoderm undergoing transition into trophoblast giant cells. Egg cylinders from 6.5-day embryos were dissected into embryonic and extraembryonic halves and cultured in suspension in vitro for up to 7 days. After 4 days, the endoderm cells of the extraembryonic fragments morphologically resemble parietal endoderm, are associated with a thick basement membrane and synthesize large amounts of the matrix proteins laminin and Type IV procollagen. A similar transition in phenotype is not seen in the endoderm of embryonic fragments, nor in visceral extraembryonic endoderm cells cultured in isolation. In another series of experiments, complete egg cylinders were dissected free of visceral endoderm overlying the extraembryonic ectoderm and then cultured in vitro. The visceral endoderm cells which recolonize the surface of the extraembryonic ectoderm develop a parietal endoderm phenotype and lay down a thick basement membrane. These results suggest that the differentiation of the extraembryonic endoderm of the early mouse embryo into visceral and parietal phenotypes can be influenced by local cell-cell or cell-substrate interactions, and is not determined solely by cell lineage.

Animals↗
PubMed1981

Hepatic induction in the avian embryo: specificity of reactive endoderm and inductive mesoderm.

Mesoderm of precardiac and cardiac region ('cardiac' mesoderm) of chick, quail and mouse embryos could induce hepatic epithelium in the endoderm of the anterior half of young quail or chick embryos (anterior endoderm) in vitro as well as in vivo. No species specificity in the induction of hepatic epithelium by the 'cardiac' mesoderm could be observed. The hepatic induction, was controlled strictly by tissue specificity of both endoderm and mesoderm. Replacement of the 'cardiac' mesoderm or the anterior endoderm by non-cardiac mesoderms or endoderms other than the anterior endoderm resulted in failure of hepatic induction. Only the anterior endoderm was found to have competence for hepatic induction, indicating that it was committed, in unknown ways, to react with 'cardiac' mesoderm, and can properly be called pre-hepatic endoderm. Comparison between the development of hepatic endoderm and the hepatic induction potency of 'cardiac' mesoderm, which was most intense during 1- to 1.5- incubation days and decreased gradually with the increase of the stage, suggests that in normal development the 'cardiac' mesoderm actually induces hepatic epithelium in the competent endoderm. Hepatic-induction potency remained up to 6 days, and was found in truncus arteriosus, ventricle and auricle areas and in endocardial and myocardial layers of the heart.

Animals↗
PubMed2003

Patterning of the hyoid cartilage depends upon signals arising from the ventral foregut endoderm.

Hyoid bone is a part of the visceral skeleton which arises from both Hox-expressing (Hox+) and Hox-nonexpressing (Hox-) cephalic neural crest cells. In a previous work, we have demonstrated that the Hox- neural crest domain behaves as a naïve entity to which the ventral foregut endoderm confers patterning cues to specify the shape and orientation of the nasal and mandibular skeleton. By using ablation and grafting approaches, we have extended our study to the formation of the hyoid bone and tested the patterning ability of more caudal levels of the lateroventral foregut endoderm in the chick embryo at the early neurula stage. In this study, endodermal stripes have first been delineated according to the projection of mid- and posterior rhombencephalic structures. The extirpation of endodermal transverse stripes along the anteroposterior axis selectively hampers the formation of the ceratobranchials and epibranchials. Thus defined, the patterning ability of the endodermal stripes was further explored in their medial and lateral parts. When homotopically engrafted on the migration pathway of cephalic neural crest cells, ventromedial zones of endoderm lead to the formation of supernumerary basihyal and basibranchial, while lateral zones generate additional cartilaginous pieces recognizable as ceratobranchial and epibranchial. Taken together, our data demonstrate that, early in development, the ventral foregut endoderm exerts a regionalized patterning activity on the cephalic neural crest to build up the primary facial and visceral skeleton in jaws and neck and enable a map of the endodermal skeletogenic areas to be drawn. This map reveals that a cryptic metamerization of the anterior foregut endoderm precedes the formation of the branchial arches.

Animals↗
PubMed2002

Pre-gut endoderm of chick embryos is regionalized by 1.5 days of development.

In this study, we set out to test the ability of endoderm from 1.5-day-old chick embryos (just before digestive tube formation) to develop region-specific characteristics when cultured heterotopically. Various parts of the 1.5-day endoderm were cultured in combination with the flank somatic mesoderm of 3- to 3.5-day chick embryos, and these cultures were analyzed for the expression of several transcription factors and the differentiation of the endoderm. By 1.5 days of normal development, the transcription factors, which are expressed in specific digestive organs, cSox2, CdxA, and cHoxb9/a13 were already expressed in the endodermal cells of the presumptive areas of their later expression domains. When 1.5-day pre-gut endoderm was cultured for 14-15 days, it showed specific differentiation into appropriate organ structures. In general, the more anterior part of the pre-gut endoderm formed the more rostral digestive organ structures while the posterior part became the caudal gut. The differentiation of these regions of endoderm matches their normal fate as recently elucidated (Matsushita [1996a] Rouxs Arch. Dev. Biol. 205:225-231; Matsushita [1999] Dev. Growth Differ. 41:313-319). Expression of cSox2, CdxA, and cHoxb9/a13 in endoderm cultured for 4-5 days is also consistent with their normal fate. Thus, each part of the pre-gut endoderm appears to be already regionally committed to some extent, in accordance with its fate by 1.5 days of development.

Animals↗
PubMed2002

Maintenance of the specification of the anterior definitive endoderm and forebrain depends on the axial mesendoderm: a study using HNF3beta/Foxa2 conditional mutants.

In mouse embryo, the early induction of the head region depends on signals from the anterior visceral endoderm (AVE) and the anterior primitive streak. Subsequently, node derivatives, including anterior definitive endoderm and axial mesendoderm, are thought to play a role in the maintenance and elaboration of anterior neural character. Foxa2 encodes a winged-helix transcription factor expressed in signaling centers required for head development, including the AVE, anterior primitive streak, anterior definitive endoderm, and axial mesendoderm. To address Foxa2 function during formation of the head, we used conditional mutants in which Foxa2 function is preserved in extraembryonic tissues during early embryonic stages and inactivated in embryonic tissues after the onset of gastrulation. In Foxa2 conditional mutants, the anterior neural plate and anterior definitive endoderm were initially specified. In contrast, the axial mesendoderm failed to differentiate. At later stages, specification of the anterior neural plate and anterior definitive endoderm was shown to be labile. As a result, head truncations were observed in Foxa2 conditional mutants. Our results therefore indicate that anterior definitive endoderm alone is not sufficient to maintain anterior head specification and that an interaction between the axial mesendoderm and the anterior definitive endoderm is required for proper specification of the endoderm. Foxa2 therefore plays an integral role in the formation of axial mesendoderm, which is required to maintain the specification of the forebrain and the anterior definitive endoderm.

Animals↗
PubMed1986

Evidence for the existence of an early common biochemical pathway in the differentiation of F9 cells into visceral or parietal endoderm: modulation by cyclic AMP.

The addition of dibutyryl cyclic AMP (dbcAMP) to aggregate cultures of F9 cells in medium containing retinoic acid (RA) directs the pathway of differentiation into parietal endoderm instead of visceral endoderm. We examined the levels of some of the markers that characterize the two pathways and studied the time of commitment of cells to either direction of differentiation by using immunoprecipitation and enzyme-linked immunosorbent assays (ELISA). For either pathway, the levels and patterns of laminin, type IV collagen, and fibronectin are the same on the first day of differentiation, characterized by slightly decreased levels of laminin and type IV collagen synthesis and an increased level of fibronectin synthesis. These levels reverse on the second day of culture when the pathways diverge markedly. The differentiation pathway, however, can be redirected into the alternate one; parietal endoderm cells become committed after 3 days, whereas visceral endoderm cells are able to change into parietal endoderm cells at any time. Thus, alpha-fetoprotein (AFP)-producing F9 embryoid bodies switched to dbcAMP-containing medium lose the capacity to synthesize AFP and start to express genes characteristic of parietal endoderm. Our results indicate that at least some visceral endoderm cells may redifferentiate into parietal endoderm cells. These phenomena thus mimic features of endoderm differentiation in the mouse embryo.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Immature endodermal teratoma of the ovary: embryologic correlations and immunohistochemistry.

Two grade 2 ovarian immature, predominantly endodermal teratomas are reported. The teratomas were in stage I and occurred in two girls, 9 and 10 years of age, who were treated with triple chemotherapy. These neoplasms differed from the usual immature ovarian teratoma as they contained no neuroectodermal components and had high alpha-fetoprotein and low human chorionic gonadotropin levels as their serum markers despite the absence of other concomitant germ cell tumors. The epithelia of the teratomas demonstrated exclusively the embryologic development of endoderm, ranging from early endoderm to tissues similar to esophagus, liver, and intestinal structures. All epithelial derivatives were positive for alpha-fetoprotein and alpha 1-antitrypsin. Liver and esophagus expressed fibrinogen, while intestine and esophagus were positive not only for carcinoembryonic antigen and chromogranins but also for thyroglobulin, thus reflecting yet another type of endodermal differentiation into thyroid. Focal human chorionic gonadotropin positivity associated with primitive intestinal and esophageal epithelia may reflect the early embryologic relationships between endoderm and trophoblast. These cases demonstrate that simultaneous alpha-fetoprotein and human chorionic gonadotropin secretion may occur in immature teratoma. The mesenchymal component also showed a wide range of differentiation, from primitive mesoblastic cells to differentiated cells, such as hemopoietic foci, smooth muscle, bone, and cartilage. Both the primitive endoderm and the mesenchyme co-expressed vimentin and keratin, reflecting their intimate developmental relationships and possibly supporting the hypothesis of mesenchyme originating from endoderm, as suggested by previous embryologic studies. Since endodermal and mesenchymal areas similar to those described here are found in association with yolk sac tumors and embryonal carcinoma, it is possible that the present cases may represent an endodermal differentiation accomplished by either of these developmentally related germ cell tumors.

Child↗
PubMed2005

Motility of endodermal epithelial cells plays a major role in reorganizing the two epithelial layers in Hydra.

Cell-cell interactions and cell rearrangements play important roles during development. Aggregates of Hydra cells reorganize into the two epithelial layers and subsequently form a normal animal. Examination of the formation of the two layers under various situations, indicates that the motility of endodermal epithelial cells, but not the differential adhesive forces of the two types of epithelial cells, plays the critical role in setting up the two epithelial layers. (1) When aggregates of ectodermal cells and of endodermal cells were placed in direct contact, the endodermal cells migrated into the interior of the ectodermal aggregate. This process was completely inhibited by cytochalasin B although initial firm attachment between the two aggregates was not blocked. (2) A single endodermal epithelial cell placed in contact with an ectodermal aggregate, actively extended pseudopod-like structures and migrated toward the center of the ectodermal aggregate. In contrast, an ectodermal epithelial cell remained in contact with an endodermal aggregate and never exhibited migratory behavior. Cytochalasin treatment of only endodermal epithelial cells abolished the migration. (3) One to 4 endodermal epithelial cells and/or ectodermal epithelial cells were placed in contact with one another forming up to 4-cell aggregates. Endodermal epithelial cells exhibited high motility that can be attributed to the migratory movement described above. Finally, formation of actin bundles, as visualized with rhodamine-phalloidin, was always correlated with pseudopod formation in endodermal epithelial cells during early and mid stages of aggregate formation.

Animals↗
PubMed2006

Fgf signaling negatively regulates Nodal-dependent endoderm induction in zebrafish.

In zebrafish development, Nodal signaling is critical for the induction of endoderm and mesoderm. Three transcription factors downstream of Nodal, Bonnie and Clyde (Bon), Faust (Fau)/Gata5 and Casanova (Cas), are required for endoderm induction. However, it is not yet fully understood how the Nodal signaling pathway regulates the decision process of endoderm and mesoderm induction. In this study, we focused on Fgf signaling, downstream of Nodal signaling, during endoderm induction. We found that activation of Fgf signaling decreases the number of cas-expressing endodermal cells. Conversely, inhibition of this signaling increases the number of endodermal cells without affecting the expression of Nodal, Nodal antagonists, bon or fau/gata5. Inhibition of Fgf signaling in endoderm mutants suggests that this signaling negatively regulates cas expression by a pathway parallel to Bon and Fau/Gata5 in the molecular cascade leading to endoderm. Furthermore, activation of Fgf signaling can overcome Cas-mediated abrogation of mesodermal gene expression. Altogether, these results suggest that Fgf signaling negatively regulates endoderm induction, possibly through repression of cas expression and down-regulation of Cas function.

Animals↗
PubMed1997

Induction of yolk sac endoderm in GATA-4-deficient embryoid bodies by retinoic acid.

GATA-4, a transcription factor implicated in lineage determination, is expressed in both parietal and visceral endoderm of the early mouse embryo. In embryonic stem cell-derived embryoid bodies, GATA-4 mRNA is first detectable at 4-5 days of differentiation and is confined to visceral endoderm cells on the surface of the bodies. Previously we reported that targeted mutagenesis of the Gata4 gene in embryonic stem cells results in a block in visceral endoderm differentiation in vitro. In an attempt to elucidate the role of GATA-4 in the formation of visceral endoderm, we have now differentiated Gata4 -/- and wild type embryoid bodies in the presence of retinoic acid +/- dbcAMP, known inducers of endoderm formation. We show that differentiation of Gata4 -/- embryoid bodies in the presence of retinoic acid results in formation of visceral endoderm, while differentiation of Gata4 -/- embryoid bodies in the presence of retinoic acid plus dbcAMP causes parietal endoderm formation. The presence of these yolk sac endoderm layers was confirmed by light microscopy and analysis of biochemical markers including alpha-fetoprotein, type IV collagen, laminin, and binding sites for Dolichos biflorus agglutinin. Treatment of Gata4 -/- embryoid bodies with retinoic acid induces expression of another GATA-binding protein, GATA-6, in both visceral and parietal endoderm cells. That another GATA-binding protein is induced in the absence of GATA-4 suggests that this family of transcription factors plays an important role in yolk sac differentiation.

Animals↗
PubMed2003

Novel gene expression domains reveal early patterning of the Xenopus endoderm.

The endoderm gives rise the respiratory and digestive tract epithelia as well as associated organs such as the liver, lungs and pancreas. Investigations examining the molecular basis of embryonic endodermal patterning and organogenesis have been hampered by the lack of regionally expressed molecular markers in the early endoderm. By differentially screening an arrayed cDNA library, combined with an in situ hybridization screen we identified 13 new genes regionally expressed in the early tailbud endoderm of the Xenopus embryo. The putative proteins encoded by these cDNAs include a cell surface transporter, secreted proteins, a protease, a protease inhibitor, an RNA-binding protein, a phosphatase inhibitor and several enzymes. We find that the expression of these genes falls into one of three re-occurring domains in the tailbud embryo; (1). a ventral midgut, (2). posterior to the midgut and (3). in the dorsal endoderm beneath the notochord. Several of these genes are also regionally expressed at gastrula and neurula stages and appear to mark territories that were previously only predicted by the endoderm fate map. This indicates that there is significant positional identity in the early endoderm long before stages 28-32 when regional specification of the endoderm is thought to occur. These new genes provide valuable tools for studying endodermal patterning and organogenesis in Xenopus.

Animals↗